Isto funciona bem para mim.
SHOW COLUMNS FROM `table` LIKE 'fieldname';
Com PHP seria algo como ...
$result = mysql_query("SHOW COLUMNS FROM `table` LIKE 'fieldname'");
$exists = (mysql_num_rows($result))?TRUE:FALSE;
SHOW COLUMNS FROM `table` LIKE 'fieldname';
$result = mysql_query("SHOW COLUMNS FROM `table` LIKE 'fieldname'");
$exists = (mysql_num_rows($result))?TRUE:FALSE;